The 73-year-old was caught by TV cameras yelling “Heil Hitler” from the back seat of a police car after he was apprehended in the parking lot of a local elementary school. Rabbi Herbert Mandl, chaplain for the Overland Park Police Department, said the gunman asked people whether they were Jewish before he opened fire. Two of the victims, named by grieving family members as Dr. William Lewis Corporon and his grandson Reat Griffin Underwood, 14, were not Jewish, however--they were members of the nearby United Methodist Church of the Resurrection.

The Southern Poverty Law Center said they had confimed Miller’s arrest with his wife, Marge, who said her husband had been drinking at a Missouri casino the night before and had not been heard from since. Marge Miller told the SPLC that authorities came to her door at 8:30 p.m. on Sunday and told her that her husband had been arrested in the shootings.

Miller, who also uses the alias Frazier Glenn Cross Jr., has an extensive résumé of hate. A former Green Beret who served in Vietnam, he embraced white supremacy in the 1970s, first joining the National States’ Rights Party and then the National Socialist Party of America—the Nazis.

According to his considerable dossier on the SPLC website Miller was forced to retire from the military due to his extremist connections. He bought a farm in Angier, North Carolina, where he formed the Carolina Knights of the Ku Klux Klan in 1980. He preferred wearing fatigues to the traditional Klan robe and recruited active-duty soldiers to conduct paramilitary-style training, aggressively seeking publicity and taking inspiration from Hitler, as he described in his autobiography: “I would try to emulate Hitler’s methods of attracting members and supporters…I placed great emphasis on staging marches and rallies. It had been successful with Hitler.” His stated goal was to create an all-white “Carolina Free State.”

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Miller’s dark ambitions with the Carolina Knights hit a legal obstacle when the Southern Poverty Law Center successfully sued him and his organization and received a consent decree requiring that they stop all intimidation against African-Americans and paramilitary activity. In 1985, Miller formed the White Patriot Party, ostensibly trying to move into the political sphere, but he was convicted of criminal contempt a year later for purchasing weapons and explosives to fund an insurgency to create a “White Southland.” He was sentenced to a year in prison but went underground while out on bond. He mailed supporters—whom he called “Aryan warriors of The Order”—establishing a point system for each murder: “Niggers (1), White race traitors (10), Jews (10), Judges (50) Morris Seligman Dees (888).” Dees is the founder of the Southern Poverty Law Center.

After the FBI tear-gassed Miller and four Klansman out of a mobile home loaded with weapons and explosives in Springfield, Missouri, Miller served three years in federal penitentiary, reducing his sentence in a plea deal by testifying against 14 other white supremacists.

In recent years, Miller ran unsuccessfully for elective offices, including the U.S. House of Representatives and the U.S Senate, receiving 23 and seven votes, respectively. His 2010 Senate campaign—for which his slogan was “It’s the Jews, Stupid”—landed him an interview on The Howard Stern Show. In response to Stern’s quip that Miller was the most “honest politician” in America because he made his beliefs crystal clear, Miller replied that U.S. politicians “are all a bunch of whores for Israel, they’re all corrupt to the core, and they’re all traitors to America.” Miller prominently displays a link to the interview on his low-budget website, Whty.org, dedicated to white supremacy and anti-Semitism, including photos of Klan rallies and extensive screeds about the Jewish control of the media.

Miller has long been a regular contributor on anti-Semitic and white supremacist Internet forum Vanguard News Network (VNN). He even took to VNN before an interview with Sacha Baron Cohen’s fictional character “Bruno”—which he later claimed he knew was a setup—boasting on a message board that he was being paid by a German TV station to “air my racist and anti-semitic ‘ravings’ far and wide.”

In 2012, Miller lectured a class at Missouri State University at the request of a professor whose class wanted to know more about white supremacists, BuzzFeed reports. “They came out of there convinced that white supremacy is a real thing and a dangerous thing,” Professor David Embree said.

The SPLC notes that such sites appear to be breeding grounds for violence. Kevin William Harpham posted on VNN before he planted an improvised explosive device along the route of the 2011 Martin Luther King Day parade in Spokane, Washington. “Our research shows that racist killers are hiding among us in plain sight,” the SPLC wrote in its report on Miller. “A forthcoming two-year study by the SPLC will show that nearly 100 people in the last five years have been murdered by active users on another prominent racist website, Stormfront.org.”

On a hate and booze bender, as hundreds of teenagers were expected to arrive for a talent competition and actors were rehearsing for a production of To Kill a Mockingbird the day before Passover, Miller apparently fulfilled his decades of threats and allegedly fired shots outside the Overland Park Jewish Community Center. Dr. Corporen was taking his grandson, an Eagle Scout and freshman at Blue Valley High School, for singing try-outs when they were struck down. "We take comfort knowing they are together in Heaven," the family said in a statement. Dr. Corporen, who was approaching his 50th wedding anniversary, was described as a “well-loved physician” in the local community.

The shooter then moved on to the Village Shalom retirement community, where a woman was killed on the scene.

Overland Police Chief John Douglass declined to release Miller’s name at a press conference Sunday, instead describing the suspect simply as a white male in his 70s who has a beard and is not from Kansas. Douglass did tell reporters that police were certain a shotgun was used in the attacks and were investigating the possibility that a handgun and an assault rifle may have been used as well. Douglass confirmed at the press conference that the FBI already had agents on the ground investigating the shootings as a hate crime.

President Obama released a statement on Sunday night, offering his thoughts and prayers to the families of the victims. “While we do not know all of the details surrounding today’s shooting, the initial reports are heartbreaking,” he said.

Correction: An earlier version of this article mistakenly said Miller has posted to Stormfront.org.